Speed control device for stepping motor

Abstract

A speed control device for stepping motor is disclosed which is possible to freely control the running speed of the stepping motor when driving it in closed loop. Its mechanism is designed to be possible to decide which excitation phase to be excited according to a phase difference between the output signals emitted from the encoder and the speed-variable reference clock signals and to make the running speed of stepping motor follow to the instruction of said reference clock signals.

What is claimed is: 
     
       1. In a system for controlling the running speed of a stepping motor, including a stepping motor encoder for providing pulse signals representative of the stepping motor position and excitation phase, a distributor, and a speed control device connected to receive the pulse signals from the encoder and delivering a pulse train to said distributor, said speed control device comprising: pulse generator means for providing a series of pulses at a selectively variable repetitive frequency;   phase detector means connected to receive the pulse signals from said encoder as a first input signal and the series of pulses from said pulse generator means at a second input signal, said phase detector means including means for detecting each phase of said first and second input signals; and   means for shifting a motor excitation phase corresponding to an excitation phase indicated by the encoder pulse signals and thereby accelerating or decelerating the running speed of said stepping motor in accordance with a difference between logic levels "H" and "L" of output signals emitted from said phase detector.   
     
     
       2. In a system to control the running speed of a stepping motor through a contrivance designed to be possible to decide which excitation phase to be excited according to the output signals emitted from an encoder connected to said stepping motor; the speed control device for stepping motor comprising of, a clock signal generating means which generates a speed-variable reference clock signals,   a phase discriminating means which makes a comparison between both phases of said reference clock signals and said output signals emitted from said encoder and gives an acceleration order if the phase of said reference clock signals leads the encoder output signals and gives a deceleration order if it lags the encoder output signals,   a rotational direction detecting means to detect the rotational direction of stepping motor through said encoder output signals,   a phase detecting means to detect the current phase of the said stepping motor through said encoder output signals,   an acceleration means to make the excitation phase, subsequent to the present phase, step forward in turn when the acceleration order is given after detection by said rotational direction detecting means that said stepping motor is rotating normally, and   a deceleration means to maintain the present excitation phase as it is whenever a deceleration order is given.   
     
     
       3. In a system to control the running speed of a stepping motor through a contrivance designed to make it possible to decide which excitation phase is to be excited according to the output signals emitted from an encoder connected to said stepping motor; the speed control device for stepping motor comprising of, a generating means of excitation pattern to be given to the said stepping motor,   a renovation means to sequentially renovate said excitation pattern,   a comparison means to compare an actual running speed of said stepping motor with an instructed speed,   a control means for changing the running speed to renovate said excitation pattern according to a difference between said actual running speed of the stepping motor and said instructed speed.